Audio electromagnetic capacity alarm device



May 24, 1955 K. H. SCHMIDT 2,709,251

. a AUDIO ELECTROMAGNETIC CAPACITY ALARM DEVICE Filed Aug. 2, 1951 @sheets-sheet 1 j INVENTOR MEA/NETA? #52AM/m' ATTORNEY ay 24, 1955 K. H. SCHMIDT 2,709,251

AUDIO ELECTROMAGNETIC CAPACITY ALARM-.DEVICE Filed Aug. 2, 1951 v 4 sheets-sheet 2 INVENTOR BY MVM/inw ATTORNEY ay 24, 1955 K H SCHM|DT 2,709,251 AUDIO ELECTROMAGNETIC CAPACITY ALJRM-DEVICE:k

Filed Aug. 2, 1951 4 sheets-sheet s INVENTOR ATTORNEY May 24, 955 K. H. SCHMIDT AUDIO ELECTROMAGNEIIC CAPACITY ALARM DEVICE 4 Sheets-Sheet 4 INVENTOR ATTORNEY Filed Aug. 2,v 1951 Maite AUDIO ELECTROMAGNETIC CAPACITY ALARM DEVICE Kenneth H. Schmidt, Danbury, Conn.

Application August 2, 1951, Serial No. 239,923

11 Claims. (Cl. 340-261) vice which includes audio signalling means and which has suiiicient capacity and sensitivity to select desired signals without going into alarm because of power line voltage fluctuations, atmospheric changes in temperature and humidity, electrostatic disturbances, such as those caused by fluorescent lights and some electric motors, or electromagnetic radiation from long wave transmitters, andthe like.

This invention is an improvement over the electromagnetic security alarm system of my copending application with the Serial No. 225,993, as in addition to the elements embodied in the above-noted application this device includes a sound-operated relay circuit which causes a light to show and a buzzer to operate in the guard signalling device whenever the sound level at the protected area is of sufcient magnitude. The audio signalling device, however, is to be considered as an adjunct to the electromagnetic security alarm system and as such does not have the emergency power provisions that would be provided were it designed as a complementary unit.

Furthermore, in the capacity alarm system of this invention the metal cabinet housing the capacity control device is not connected into the antenna circuit to provide electromagnetic protection for the cabinet. Where complete perimeter protection is provided, connecting the cabinet in the antenna circuit is not too important. However, where object protection only is provided, the metal cabinet must be positioned close to sensitive radiating strips in the antenna circuit in order to provide the additional protection necessary for absolute security.

The purpose of this invention is to further improve proximity or capacity alarm devices by providing sound in combination whereby it is possible to protect areas or objects which have more actual, measurable capacity to earth ground with greater sensitivity and selectivity, more freedom from false alarm, and in which less supervision by service organizations is required, and which, in conjunction with other apparatus relating to this invention, provides an audio signal and thereby provides a still greater measure of security for the protection of valuable objects, equipment and property.

The principle of detection by utilizing the human body as a conductor of radio frequency electrical current is not new. However, the system included in these inventions is an improvement over other proximity alarm devices as it is an electromagnetic security alarm system that is not susceptible to false alarms and that is not adapted to be comprised or nullied.

An electromagnetic security alarm system is inherently more secure than other systems operating by direct cur- 2,709,251 Patented May 24, 1,955

'ire

rent foil and contacts, or photo-electric principles and the like, because it can signal the approach of the intruder by utilizing the electromagnetic radiation from the antenna and/or protected objects, and by combining the audio signal still further security is provided because the tampering of an intruder with parts not connected in the antenna circuit can be detected. The improved electromagnetic alarm device of this invention, therefore, not only does not permit an intruder to get close enough to the antenna and/or protected objects to tamper with the antenna or objects, but also prevents tampering with objects or parts not directly associated with the antenna by sending a signal to the guard which informs him of the generation of noise in the protected area.

The object of this invention is, therefore, to achieve a still higher degree of security for valuable objects and vital areas, and with this thought in mind this invention includes the audio signalling instrumentalities whereby in addition to providing a capacity alarm device having high sensitivity and that can not be comprised or nulliied even by persons having intimate knowledge of the physical and electrical constructions provides means for detecting the slightest sound in a protected area.

Another object of the invention is to provide more protection against bodily harm for the guard responding to the alarm and an improved opportunity to apprehend the intruder by permitting the guard to listen to the sounds of the intrusion and to act accordingly.

A further object of the invention is to provide Aa capacity alarm system having audio signalling means therein in which the parts are of conventional designs and the apparatus is of comparatively simple and economical construction.

Other features and advantages of the invention will appear from the following description taken in connection with the drawings, wherein:

Figure l is an elevational view illustrating the position of the microphone in the cabinet in which the apparatus is installed.

Figure 2 is a front elevational view of the guard signalling device showing the position of the loud speaker, the bell silence, push-to-listen, and Day-Night switches, and also the positions of the lights corresponding with the switches.

Figure 3 is a general elevational view illustrating the relative positions of the elements in the cabinet, with the wiring and other parts omitted.

Figure 4 is a view showing a wiring diagram of the parts of my copending application with the audio signalling device incorporated therein.

Figure 5 is a view also showing a wiring diagram, and illustrating the audio signalling elements incorporated in the guard signalling device.

Referring now to the drawings wherein like reference characters denote corresponding parts the audio signalling device of this invention is incorporated in the electromagnetic security alarm system of my copending application which includes an independent circuit that is supplied with batteries 10 and 11, and these batteries furnish filament and anode voltage for the electron tubes. By operating the device independent of Ia power line, no complicated voltage stabilization circuits or emergency stand-by power is required. The circuit is provided with a conventional oscillator tube 12 which, operating on approximately 30 kc./s., supplies radio frequency energy to a capacity bridge. In this system the choice of oscillator frequency is important. Lower frequencies permit the use of longer antennas having more capacity to earth ground, and which provide good sensitivity, although they handicap, somewhat, the ability of the device to reject electrostatic and electromagnetic interfering signals, the

' to earth ground.

The voltage output from the capacity bridge varies with antenna capacity. At the null point, the capacity bridge is balanced, and either an increase or decrease in capacity causes an increase in voltage output from the bridge which when amplified by tube v18, rectified by germanium crystal 19, passed through time delay condenser 20, and sensitive relay 21, produces the alarm. Highly selective tuned circuits 22 and 23 precede the grid of the first amplifier tube 18, or rectifier if the amplifier stage is not required. The purpose of the transformer including the windings 22 and 23 is to filter out any interfering electrostatic and/or electromagnetic energy picked up by the antenna. Another important reason for using the capacity bridge as the detecting device is that the bridge makes it possible to isolate the grids of both of the tubes 12 and 18, from the antenna through the use of high Q input and output transformers.

- The potentiometer 24, which is the sensitivity control, being positioned in the circuit at this pointv provides the greatest measure of stability when maximum sensitivity `is not required.

Tube 18 is a conventional radio frequency pentode amplifier with a high Q parallel resonant plate load tuned to the oscillator frequency, and rectifier 19 is a sensitive germanium crystal which is placed in ,a low impedance circuit to avoid its rectifying directly electrostatic interfering signals.

RC network 25, having a time constant of approximately one second, provides still another method of filtering out electrostatic interference. Sharp impulses, such as are produced by lightning and other atmospheric causes are filtered through RC combination 25, which includes a resistance 26 and a condenser 27, and this improvement also results in greater freedom from false alarms.

In this circuit, including germanium crystal 19, delay condenser 20, sensitive relay 21 and the RC network 25, it will be understood how an alarm is produced by either an increasing or decreasing signal. signal, current is made to fiow through time delay condenser and relay 21, and the current will continue to flow until the voltage across the condenser 20 assumes its new, higher steady-state value, and with a decreasing signal energy in the condenser 20 is released into the circuit y of RC combination or network 25 and relay 21, the current now flowing in the Iopposite direction to that of the current in the condition of the increasing signal. Capacity alarm devices which can produce an alarm on either an increasing or decreasing signal are considered more secure vthan devices which produce the alarm with only an increasing signal, or with only a decreasing signal. In the system of these inventions the alarm is also produced upon failure of either the filament battery 10, or the anode battery l1, these batteries being the only ones delivering energy during the protection period.

Relay 21 is a latching type relay which, when it is actuated or goes into alarm, is latched and remains in alarm even though the relay coil or solenoid is deenergized.

Relay28 is a slave relay which operates from alarm relay 21, and relay 29 is a time delay relay which permits the operator to leave the protected area without causing an alarm.

The circuit is provided with an eight pole, four position switch 30 which provides a test position to make it` con- With an increasing y -it is utilized for full protection.

In addition to including these elements of the capacity alarm system of my copending application the system of this' invention includes a sound-operated relay circuit which causes a light to show and -a buzzer to operate in the guard signalling device when the sound level at the protected area is of sufiieient magnitude. The audio signalling device, however, is to be considered as an adjunct to the electromagnetic security alarm system and as such does not have the emergency power provisions that would be provided were it designed as a complementary unit.

As shown in the wiring diagram in Figure 4, a microphone 3l is connected by a wire 32 to the input of a two stage audio amplifier utilizing miniature tubes 33 and 34. The audio outputis matched to line impedance through the use of a transformer 35, and fed into the :alarm line through blocking condensers 36 and 37.

The transformer is connected in the telephone'line connecting this device with theguard signalling device, with the side in which the condenser 36 is positioned connected to the positive terminal 38 through wires 39 and 40, and the side in which the condenser 37 is positioned connected to the negative terminal by wires 41 and 42. The line to the negative terminal 43 being provided with a tamper switch 44 and a resistor 45, and the line to the positive terminal being provided with an alarm light 46.

The filament and plate voltage for the audio section of the system is furnished through a conventionahpower supply as indicated by the numeral 47, and the power supply is connected to the switch 30 with wires 48 and 49. The wire 49 is provided with a fuse 50.

The guard signalling device together with the audio alarm circuit, as illustrated in Figure 5, includes a network 51 comprising a group of fixed and variable resistors forming a Wheatstone bridge, one arm of which is the combination of the lumped resistance of resistor of the capacity alarm circuit and the distributed resistance of a telephone line connecting the devices.

The bridge is brought into balance with rheostats 52 and 53, and bridge balance is indicated by ultrasensitive galvanometer relay 55. Energy is supplied to the bridge by a battery, such as a six volt primary cell. The telephone line is'maintained under very sensitive balance, the sensitivity being selected by varying sensitivity control 54 which shunts the microampere relay 55. At maximum sensitivity the total change in resistance or current required to cause an alarm is less than 1%. With this delicate balance leakage of current from other telephone lines brought out on the same terminal hoard may call the guards attention by ringing a bell and lighting a lamp, and this may be caused by unbalancing of the ultra-sensitive relay 55 which operates slave relay 57, sending current into lamp 58 and annunciator 59 through switch 60. In this alarm system currents are balanced to such an extent that the presence of an intruder in an area influences one side of the circuit so that an element is unbalanced and a circuit is completed to send an alarm signal. By this means other circuits, such as a telephone circuit on a control board may inuence one side of a circuit and thereby send a signal to give an alarm.

With the audio signal incorporated in the guard signalling device, as shown in Figure 5, an input transformer 61 in the guard signalling device for matching said audio signal from line to grid impedance and volume control 62 adjusts the volume of sound emanating from the speaker. .The tube 63 is an audio power amplifier for driving the speaker and germanium crystal 64 rectities the audio and applies the D. C. signal through relay sensitivity control 65 to the two stage D. C. amplifier, indicated by the numerals 66 and 67. Relay 68 is a double pole relay which may be of the momentary-operating type, as shown, or it may be converted into the latching type by utilizing an eXtra set of contacts. I

The bell-silence switch 60 automatically turns on the speaker when the bell is silenced after an alarm so that the guard may listen to the sounds of the intrusion and gain some knowledge of what to expect when he makes his investigation of the protected area. The guard may at any time make a listening check of the protected area by depressing the spring-return push-to-listen switch 70. Should the sounds of the room cause the buzzer to operate, the buzzer may be silenced by depressing the listen switch 70.

The filament and plate voltage for the tubes is furnished through a conventional power supply, as indicated by the numeral 71.

By thismeans slight sounds caused by an intruder tampering with a door, window, filing cabinet, desk or safe are picked up by the microphone 31, Figure 4, and transmitted to the guard signalling circuit, where they com-y plete a circuit to a light and operate a buzzer, and by pressing a button the guard may silence the buzzer and listen. f,

With the parts arranged in this manner the capacity control device is incorporated in a cabinet 72, Figure l,

. with an opening 73 in one side for the microphone, and

the guard signalling device, which is illustrated in Figures 2 and -3 is provided with a cabinet 74 having a door 75 on the inside of which the loud speaker 76 is mounted. j

The door is also provided with a plurality of small windows with lights behind the windows wherein a light 77 shows in a window 78 to indicate that the line has been tampered with, a light 79 shows in a window 80 to indicate that the system is set for day operation, a light 81 shows through a window 82 for night operation, a light 83 shows through a window 84 to show that an alarm is on, and a light 85 shows through a window 86 to indicate that the buzzer is operating.

`The cabinet 74 is provided with an adjusting screw 87 v for sensitivity, similar screws 88 and 89 for day and night balancing, respectively, a similar screw 90 for relay sensitivity, and a screw 91 foivvolume. The cabinet also shows relative positions of other parts for mounting and adjusting the elements of the device.

vhaving batteries therein connecting the sensitive relay to the bridge, an antenna extended from the bridge, a microphone positioned in a protected area, an alarm line connectingthe microphone to said circuit of the sensitive relay and bridge, and means feeding the amplified output ot' the microphone into the alarm line. 2. A capacity alarm device comprising a ratio potentiometer, a powerV factor rheostat, and a condenser providing a capacity bridge, means for supplying radio frequency current to the bridge, a sensitive relay connected to the bridge and adapted to provide an alarm upon unbalancing of the bridge, an antenna extended from the bridge, a microphone positioned in a protected area and connected to the input of a two stage audio amplifier, an alarm line connecting the microphone to said circuit of the sensitive relay and bridge, a transformer for matching the audio output of the microphone to the impedance of the alarm line, blocking condensers in the connections of the transformer to the line, and a power supply for the lament and plate voltage of the audio amplifier.

3. A capacity alarm device comprising a ratio potentiometer, a power factor rheostat, and a condenser providing a capacity bridge, an oscillator tube for supplying radio frequency current to the bridge, a sensitive relay for producing an alarm upon unbalancing of the bridge, an antenna extended from the bridge, a microphone positioned in a protected area, a two stage audio amplifier to the input ofwhich the microphone is connected, an alarm line connecting the microphone to said circuit of the sensitive relay and bridge, a transformer for matching the audio output of the microphone to the impedance of the alarm line, blocking condensers in the connections of the transformer to the line, a power supply for the filament and plate voltage of the audio amplifier, a guard signalling device including a Wheatstone bridge connected to the capacity bridge through a telephone line, rheostats in the guard signalling device for bringing the bridge thereof into balance, an ultra-sensitive galvanometer relay for indi` eating the balance of the bridge of the guard signalling device, an input transformer in the guard signalling device for matching said audio signal from line to grid impedance, a loud speaker in the guard signalling device, and an audio power amplifier in the guard signalling device for driving the speaker.

4. A capacity alarm device as described in claim 3, wherein the guard signalling device includes a two stage D. C. amplifier and a germanium crystal for rectifying the audio and applying the D. C. signal through a relay sensitivity control to the amplifier of the guard signalling device.

5. A capacity alarm device as described in claim 3, wherein the guard signalling device includes .a volume control for adjusting the volume of sound emanating from the speaker, a bell silence switch for automatically turning on the speaker should a bell in the system be silenced, and a power supply for furnishing filament and plate voltage for the tubes of the guard signalling device.

6. A capacity alarm device as described in claim 3, which uses in combination a sound-operated relay circuit, a two conductor line to convey the signal from the protected area to the guard area, a rectifier, a momentary-operating or latching-type relay to signal .the guard by audiovisual method, and a loudspeaker.

7. A capacity alarm device having a protected` area and a guard area, a capacity bridge including a ratio potentiometer, a power factor rheostat, and a condenser, an oscillator for supplying radio frequency current to the bridge, a sensitive relay connected to the bridge and adapted to provide an alarm upon unbalancing of the bridge an antenna connected to the bridge for sending signals from the protected area to the capacity bridge, a sound-operated relay circuit including a microphone, an amplifier to which the microphone is connected, a two conductor line connecting the microphone to said circuit of the sensitive relay and bridge for conveying signals from the protected area to the guard area, a rectifier positioned in a`1ow impedance circuit of the circuit from the bridge, a momentary-operating relay for signaling the guard by audiovisual means, a

vpush-to-listen switch for making a listening check of the protected area and for silencing the guard signaling means, a loudspeaker, and a circuit connecting the loudspeaker to the guard signalling device.

8. A capacity alarm device having a protected area and a guard area, a capacity bridge including a ratio potentiometer, a power factor rheostat, and a condenser, a sound-operated relay circuit including a suitable transducer, an amplifier', a two conductor line connecting the microphone to said circuit of the sensitive relay and bridge for conveying signals from the protected area to the guard area, a rectifier positioned in a low impedance circuit of the circuit from the bridge, a latching relay for signaling the guard by audiovisual means, a push-to-listen switch for making a listening check of the protected area and for Lsilencingthe guard signaling means, a loudspeaker, and a circuit connecting the loudspeaker to the guard signalling device.

9. A capacity alarm device having a protected area and a guard area, a capacity bridge including a ratio potentiometer, a power factor rheostat, and a condenser, an oscillator for supplying radio frequency current to the bridge, a Sensitive relay connected to the bridge and adapted to provide an alarm upon unbalancing of the bridge, means for supplying radio frequency current to the bridge, a sensitive relay for providing an alarm upon unbalancing of the bridge, a circuit having batteries therein in which the sensitive relay is connected, an antenna extended from the bridge to the protected area, a sound-operated relay circuit comprising a suitable transducer, an amplifier, a two conductor line for conveying a signal from the protected area to the guard area, a rectifier positioned in a low impedance circuit of the circuit from the bridge, a momentaryoperating relay for signaling a guard in the guard area by audio-visual methods, a push-to-listen switch for making a listening check of the protected area and for silencing the guard signaling means, a loudspeaker and a circuit connecting the loudspeaker to the guard signalling device.

10. In a capacity alarm system, the combination which comprises a capacity bridge balanced by a ratio potentiometer, a power factor rheostat, and a standard condenser,an oscillator for supplying radio frequency current to the bridge, a sensitive relay connected to the bridge and adapted to provide an alarm upon unbalancing of the bridge a protected area, an antenna extended from the capacity bridge to the protected area, an earth ground extended from the bridge, a sound` operated relay circuit comprised of a microphone, an amplifier, a guard area, a line connecting the microphone to said circuit of-the sensitive relay and bridge for conveying a signal from the protected area to the guard area, a rectifier positioned in a low impedance circuit of the circuit from the bridge, a momentaryoperating relay for signaling a guard in the guard area by audio-visual means, a push-to-listen switch for making a listening check of the protected area and for silencing the guard signaling means, a loud speaker, and a circuit connecting the loudspeaker to the guard signalling device.

11. The combination with a capacity alarm system having a capacity bridge and a guard system having a Wheatstone bridge, of a sound operated relay circuit comprising, a suitable transducer, an amplifier, a two conductor line for conveying a signal to the guard system, and a momentary-operating relay for actuating audio-visual means for signaling a guard, a loudspeaker, and a circuit connecting the loudspeaker to the guard system.

References ICited in the le of this patent UNITED STATES PATENTS 665,801 Rough Jan. 8, 1901 1,547,873 Hopkins Julyv28, 1925 2,428,290 Peck Sept. 30, 1947 2,499,177 Baughman Feb. 28, 1950 

